Improving the Foundation Layers for Pavements: Pavement Foundation Layer Reconstruction – Iowa I-35 Field Study - TPF-5(183)

(2016) Improving the Foundation Layers for Pavements: Pavement Foundation Layer Reconstruction – Iowa I-35 Field Study - TPF-5(183). Transportation, Department of

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Abstract

This technical project report is one of the field project reports developed as part of the TPF-5(183) and FHWA DTFH 61-06-H00011:WO18 studies. This report presents results and analysis from a field study conducted on interstate highway I-35 in Iowa. The project involved removal of the existing pavement and undercutting down to the new subgrade elevation, and placing 305 mm (12 in.) of special backfill on the subgrade as subgrade treatment and 152 mm (6 in.) of granular subbase. The new PCC pavement was 292 mm (11.5 in.) in thickness. The granular subbase material consisted of both virgin crushed limestone aggregate and recycled portland cement concrete material. The subbase layer construction process involved placing the material and compacting the layer with a smooth drum roller in a non-vibratory mode for a maximum of three passes followed by trimming process to trim the layer to the design grade. The main objective of this field study was to investigate the impacts of vibratory versus static mode of compaction and number of compaction passes on the granular subbase layer material properties such as material fines content, dry density, elastic modulus, California bearing ratio, modulus of subgrade reaction, and saturated hydraulic conductivity. Results from the field testing were analyzed using statistical t-tests to assess whether statistically significant differences exist between untrimmed and trimmed base layers and between low amplitude versus static compaction. The field test results indicated that the use of low amplitude vibration instead of the static mode of compaction can result in material degradation, as evidenced by increases in fines contents, but the resulting fines content were within the specified gradation limits. However, the trimming process resulted in much higher fines content, which in turn resulted in a denser and stiffer subbase layer but also decreased permeability values.